2006 Infiniti G35 base sedan

My check engine light comes on intermittently.  I have a stored code P2A00.  My question is whether the light should always be on if there's a stored code or does it only come on in real-time while a condition exists.  I replaced the offending upstream O2 sensor but that didn't seem to help much until I added a can of ATS 505CRF to a half tank of fuel.  Now the check engine light comes on intermittently.  Any thoughts on diagnosing the causes of P2A00 would also be appreciated.  I'm thinking of trying another fuel treatment, maybe have the bank 1 injectors checked.  I should also note that I have an oil consumption problem with this vehicle and use about a quart every 250-300 miles.  Probably stuck oil rings.  I just tried the ATS 505CRO oil treatment a few days ago but can't say yet if it helped with the oil consumption.